This invention relates to a method of making a wheel assembly from a wheel and a bearing and to the assembly product. In particular, it relates to molding a pulley having an opening at its center, positioning a bearing in the opening while the pulley is still hot, and allowing the pulley to cool so that it shrinks around the bearing and holds the bearing in place.
At the present time, pulley assemblies, consisting of a plastic pulley and a metal bearing, are made by placing a bearing in a mold and molding the plastic around the bearing. Since a bearing in the mold is held at the molding temperature during molding, heating the bearing is unavoidable. The high molding temperatures damage the grease and seals in the bearing, reducing the life of the bearing. Also, when the plastic shrinks, it exerts a considerable and often nonuniform force upon the bearing. This force warps and distorts the bearing so that it becomes out-of-round, again reducing the life of the bearing. The damage caused to the bearing by the shrinking plastic is difficult or impossible to control because the amount of shrinking is a property of the plastic material used and the method of molding.